Catálogo de publicaciones - revistas

<jats:p> When did life first appear on Earth? Previous efforts to answer this fundamental question have found early life as far back as 3450 million years ago, in rock formations in Australia. In his Perspective, Holland discusses data recently published by Mojzsis <jats:italic>et al</jats:italic> . in the journal <jats:italic>Nature</jats:italic> that pushes the earliest life back to more than 3850 million years ago. </jats:p>

<jats:p> Chemists have long sought to duplicate the rich chemistry of carbon compounds with the related elements silicon and germanium. In his Perspective, Schleyer discusses work published in the same issue by Sekiguchi <jats:italic>et al</jats:italic> . ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="60" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5296.60" xlink:type="simple">p. 60</jats:related-article> ) in which free cations containing germanium, an elusive target of organic chemists, have been synthesized. </jats:p>

<jats:p>Hull outlines how immunization programs for children have had positive political effects throughout the world.</jats:p>

<jats:p> In a report in this issue of <jats:italic>Science</jats:italic> , Shirakawa <jats:italic>et al</jats:italic> . ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="77" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5296.77" xlink:type="simple">p. 77</jats:related-article> ) show an inverse relation between exposure to the bacterium that causes tuberculosis and the incidence of asthma, leading to the proposition that childhood infections can protect against later development of asthma and similar allergic reactions. In their Perspective, Cookson and Moffatt explain the immunological basis of this proposition and discuss its implications. </jats:p>

<jats:p>Guanine nucleotide-binding proteins (G proteins) transduce a very large number of cellular regulatory signals. Several recent papers have shown that the larger heterotrimeric G proteins are regulated by a class of molecules known as the RGS proteins (regulators of G protein-signaling family) that are analogous to the GAPs (GTPase activating proteins), which regulate small monomeric G proteins. Iyengar summarizes this evidence and discusses the mechanism of action of the RGS proteins.</jats:p>

<jats:p>Chemical separations of many biomolecules and pharmaceuticals are limited by their electrostatic interaction with the surfaces of the separation medium. Mixed self-assembled monolayers of octadecyl and methyl chains organize into a dense, two-dimensionally cross-linked network over the chromatographic silica surface to reduce acid dissociation of the surface silanols. Molecular models predict that two-dimensional cross-linking is sterically possible for pure methylsiloxane monolayers, silicon-29 nuclear magnetic resonance measurements show that cross-linking predominates for mixed monolayers of primarily methylsiloxane, and chromatographic measurements confirm that electrostatic interactions are reduced when the monolayer is primarily methylsiloxane. Chromatographic separation of genetic variants of a highly charged protein, cytochrome c, demonstrates the promise of self-assembled monolayers in separations of biomolecules.</jats:p>